Cultured amniotic fluid cells provide the most accurate source of hexosaminidase A (hex A) for the prenatal detection of Tay-Sachs disease. This diagnostic tool, i.e. cell culture, has several drawbacks: 1) occasional failure of cell growth, 2) possible contamination by maternal fibroblasts, and 3) time (2-3 weeks) for cell culture before enzyme assay can be done. The first aim of this research will be to evaluate the use of hex A determinations in cell-free amniotic fluid for the accurate prenatal diagnosis of Tay-Sachs disease. The results of these studies will indicate if, and under what circumstances, amniotic fluid hexosaminidase A determinations are valuable in the prenatal detection of Tay-Sachs disease. The second aspect of this research will be to elucidate what may be the more basic defect in Tay-Sachs disease. Theoretically hex A can be synthesized from hexosaminidase B (hex B) by the addition of N-acetyl neuraminic acid (NANA). I.e. Hex B plus NANA yields Hex A. (Conversely hex A can be converted back to hex B by incubation with neuraminidase.) The third aim of this research will be to study thiamine metabolism in patients with subacute necrotizing encephalomyelitis (SNE), by utilizing fibroblasts cultured from patients with SNE. This will be done both by studying the fate of radioactively labeled thiamine administered to such tissue cultures, and analyzing such cultures for the inhibitor to thiamine pyrophosphate-adenosine triphosphate phosphotransferase. Demonstration of a specifically abnormal thiamine metabolism in fibroblasts will provide a laboratory test for the accurate diagnosis of this disorder.